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Fil: Saleta, Martin Eduardo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche | Comision Nacional de Energia Atomica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche.; Argentina. Comision Nacional de Energia Atomica. Gerencia del Area de Energia Nuclear. Instituto Balseiro; Argentina

The control of the size of bimagnetic nanoparticles represents an important step toward the study of fundamental properties and the design of new nanostructured magnetic materials. We report the synthesis and the structural and magnetic characterization of bimagnetic CoO/CoFe2O4 core/shell nanoparticles. The material was fabricated by a seed-mediated growth high-temperature decomposition method with sizes in the range of 5-11 nm. We show that the core/shell morphology favours the crystallinity of the shell phase, and the reduction of the particle size leads to a remarkable increase of the magnetic hardening. When the size is reduced, the coercive field at 5 K increases from 21.5 kOe to 30.8 kOe, while the blocking temperature decreases from 388 K to 167 K. The size effects on the magnetic behaviour are described through a phenomenological model for strongly ferri-/antiferromagnetic coupled phases.